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S
Suntower
Participating Frequently
December 20, 2013
Question

Varying Speed Of Fractal Noise Ocean Waves With Expressions

  • December 20, 2013
  • 1 reply
  • 2424 views

Hi,

Possible Noob question:

I've been following:

  http://allbetsareoff.com/2009/06/ocean-water-effect/

The video results are here: http://vimeo.com/5384704

He uses the Fractal Noise plug-in to make the water and the sky. Starting at 9:45 or so he talks about using an Expression in the 'Offset Turbulence' to create a certain 'speed' of the water.

Programming variables I understand, but I am a total noob when it comes to AE expression variables. The expression he uses is:

X = effect("Fractal Noise")("Offset Turbulence")[0];

[X, time*190]

So it seems like varying the number 190 increases or decreases the speed of the waves.

What I would like to do is have the speed -accelerate- over time. The entire video is going to be prox. 3:25. I was hoping there was something akin to keyframes I could use to make it -very- slow in the beginning, then at a certain point, quicken, then at another point -really- speed up and then finally, slow down again... independent of the sky.

If this is not easily done, I suppose I can render the sky and water separately and use keyframes in Premiere to speed up/slow down, but I figured I'd use this as a learning opportunity.

SO: Is there a way to assign a variable to that 'constant' value (190) which is based on the time position? Pseudo Code:

X = effect("Fractal Noise")("Offset Turbulence")[0];

[X, time* if(CurrentPositionInSeconds<200) ? 190 : 60]

Ideas?

 

TIA,

---JC

This topic has been closed for replies.

1 reply

Dan Ebberts
Community Expert
Dan EbbertsCommunity Expert
Community Expert
December 23, 2013

Trying to increase speed in an expression will ususally lead to disappointing results. The problem is that the expression has no memory of what has happened in the past, so at each frame, the result you get will be the same as if the speed had always been at the current value, which leads to unexpeded results, like things coming to a stop and backing up, even though the speeds are always positive. If you want to go down this road, the key is to create an expression that calculates distance by integrating all the previous speed segments. It's not too bad if you use linear keyframes, more complicated if you don't. This article explains it better:

http://www.motionscript.com/articles/speed-control.html

Dan

S
SuntowerAuthor
Participating Frequently
December 23, 2013

Thanks for the reply. I figured no one had answered because it was too stupid/obvious for words.

What I've done in the meantime is render 6 versions of the 'movie'... 3 speeds of the sky and 3 speeds of the water. And now I'm trying to 'blend' them in Premiere. It'll probably work.

My concern is that, since rendering the whole deal takes 1:30, it's a bit annoying to experiment and find it doesn't work. What I mean is that, with my machine, the RAM Preview is dodgy at best so I doubt I could see whether or not my expressions were accelerating smoothly or not. So if I can't predict what will work I'll probably stick with the above---even though it's not ideal.

I'll read the article before saying more,

Thanks!

---JC

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